Spike Branching in Wheat and Barley

The non-branched inflorescence axis is one of the most noticeable characteristics of wheat and barley compared with other grasses like rice and maize. So far, inflorescence branching within the tribe Triticeae is not well understood, and no branching mutants from barley or branched wheats have been molecularly identified. Our wheat collection with distinct spike phenotypes includes mutants with branched inflorescences which show indeterminate spikelet growth, i.e. loss of terminal spikelet formation. The branched spike phenotype, mainly occurring in tetraploid wheats (Triticum turgidum L. convar. compositum (L.f.) A. Filat.) and sometimes also known as ‘Miracle or Egyptian Wheat’, ‘Wunderweizen’ or ‘Blé d’Osiris’, develops first order branches with additional, completely fertile spikelets preferentially at the base of the spike. Moreover, such spikes often produce more than one spikelet per rachis node, resulting in double or even triple spikelet development (supernumerary spikelets). The branched-spike phenotype is of particular interest to our research group since it might deliver one approach for increasing spikelet and floret numbers per spike in wheat by modulating an important grain yield component. The inflorescence mutants, known as compositum-type in barley, show spikes with elongated rachillas that similarly occur in the basal part of the spike and form rachis-like branches. In order to elucidate inflorescence branching in Triticeae we utilized available whole-genome sequences of grasses like rice, maize and Brachypodium for mapping, molecular marker development and candidate gene approaches. The latest results on the phenotypic analyses of the early development of branching and more detailed mapping will be presented.